1. Field of the Invention
The present invention relates generally to determining data amounts for scheduled and autonomous transmission with a user equipment.
2. Description of the Related Art
A 3rd generation mobile communication system using Wideband CDMA (WCDMA) based on the European Global System for Mobile communications (GSM) system and General Packet Radio Services (GPRS), Universal Mobile Telecommunication Service (UMTS) provides mobile subscribers or computer users with a uniform service of transmitting packet-based text, digitized voice, and video and multimedia data at or above 2 Mbps irrespective of their locations around the world.
Particularly the UMTS system uses a transport channel called the E-DCH in order to further improve the packet transmission performance of uplink communications from a UE to a Node B (interchangeable with a base station). For more stable high-speed data transmission, Adaptive Modulation and Coding (AMC), Hybrid Automatic Repeat reQuest (HARQ), Node B-controlled scheduling, and shorter Transmission Time Interval (TTI) were introduced for the E-DCH transmission.
AMC is a technique of determining a Modulation and Coding Scheme (MCS) adaptively according to the channel status between the Node B and the UE. Many MCS levels can be defined according to available modulation schemes and coding schemes. The adaptive selection of a MCS level according to the channel status raises efficiency of resource usage.
HARQ is a packet retransmission scheme for retransmitting a packet to correct errors in an initially transmitted packet. HARQ is branched into Chase Combining (CC) and Incremental Redundancy (IR).
Node B-controlled scheduling is a scheme in which the Node B determines whether to permit E-DCH transmission for the UE and if it does, and an allowed maximum data rate, and transmits the determined data rate information as a scheduling grant to the UE, and the UE determines an available E-DCH data rate based on the scheduling grant.
Shorter TTI is a technique for reducing retransmission time delay and thus increasing system throughput by allowing the use of a shorter TTI than the shortest TTI of 10 ms for a conventional Dedicated CHannel (DCH).
FIG. 1 illustrates uplink packet transmission on the E-DCH in a conventional mobile communication system. While the E-DCH and CDMA communication systems are discussed in detail along with its problems, similar problems may also arise in other communication systems including but not limited to OFDMA and TDMA systems, and the present invention may be applied in any one of those communication systems.
Referring to FIG. 1, reference numeral 100 denotes a Node B supporting the E-DCH and reference numerals 101 to 104 denote UEs using the E-DCH. As illustrated, the UEs 101 to 104 transmit data to the Node B 100 on E-DCHs 111 to 114.
The Node B 100 notifies the individual UEs 101 to 104 whether they are permitted for E-DCH transmission or transmits to the UEs scheduling grants indicating E-DCH data rates for them, based on information about buffer occupancy and requested data rates or channel status information received from the UEs. The scheduling is performed such that the Rise over Thermal (RoT) measurement of the Node B does not exceed a target RoT to increase total system performance by, for example, allocating low data rates to remote UEs (e.g. the UEs 103 and 104) and high data rates to nearby UEs (e.g. the UEs 101 and 102).
FIG. 2 is a diagram illustrating a conventional signal flow for message transmission and reception on the E-DCH in an exemplary embodiment of the present invention.
Referring to FIG. 2, a Node B 200 and a UE 201 establish an E-DCH in step 202. Step 202 involves message transmission on dedicated transport channels. The UE 201 transmits scheduling information to the Node B 200 in step 204. The scheduling information may contain uplink channel status information being the transmit power and power margin of the UE, and the amount of buffered data to be transmitted to the Node B 200.
In step 206, the Node B 200 monitors scheduling information from a plurality of UEs to schedule uplink data transmissions for the individual UEs. The Node B 200 decides to approve an uplink packet transmission from the UE 201 and transmits scheduling assignment information to the UE 200 in step 208. The scheduling assignment information can be an Absolute Grant (AG) indicating an allowed maximum data rate and an allowed transmission timing, or a Relative Grant (RG) indicating up/hold/down in an allowed maximum data rate.
In step 210, the UE 201 determines the Transport Format (TF) of the E-DCH based on the scheduling assignment information. The UE 201 then transmits to the Node B 200 the TF information and uplink packet data on the E-DCH at the same time in steps 212 and 214. The UE 201 selects an MCS level according to an allowed maximum data rate set by the Node B 200 and its channel status, and transmits the E-DCH data using the MCS level in step 214.
The Node B 200 determines whether the TF information and the uplink packet data have errors in step 216. In the presence of errors in either of the TF information and the uplink packet data, the Node B 200 transmits a Negative ACKnowledgement (NACK) signal to the UE 201 on an ACK/NACK channel, whereas in the absence of errors in both, the Node B 200 transmits an ACK signal to the UE 201 on the ACK/NACK channel in step 218. In the latter case, the packet data transmission is completed and the UE 201 transmits new packet data to the Node B 200 on the E-DCH. On the other hand, in the former case, the UE 201 retransmits the same packet data to the Node B 200 on the E-DCH.
Under the above-described environment, if the Node B can receive from the UE scheduling information including information about the buffer occupancy and power status of the UE, it allocates a low data rate to the UE if it is far from the Node B, is in a bad channel status, or has data of a lower service class. If the UE is near to the Node B, is in a good channel status, or has data of a higher service class, the Node B allocates a high data rate to the UE. Therefore, the total system performance is increased.
Aside from the Node B-controlled scheduling, autonomous transmission or non-scheduled transmission is also supported for the E-DCH. The autonomous transmission obviates the need for transmitting scheduling information to the Node B and receiving scheduling assignment information from the Node B in the UE. Therefore, rapid E-DCH transmission is possible. While the E-DCH and CDMA communication systems were discussed above along with its problems, similar problems may also arise in other communication systems including but not limited to OFDMA and TDMA systems, and the present invention may be applied in any one of those communication systems.